The Stain - Page 14

I think the brightness of the images does not reflect the absolute luminosity; it is affected by the brighness of the background. Like a consumer camera where the shutter size is automatically regulated to prevent overexposure or underexposure.

When I looked at the early filter images of the deck, it appeared to me they were darker in blue than in infrared---the opposite of the stain, but that may have been due to variable exposure.

Psych

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Reply: 262

Posted: April 29, 2011 8:23 PM

"I think the brightness of the images does not reflect the absolute luminosity; it is affected by the brightness of the background. Like a consumer camera where the shutter size is automatically regulated to prevent overexposure or underexposure."

True. However, are not the blue and green channel overexposed in the rover images due to minimal blue and green emissions? Would this not result in brighter blue and green areas in the B\W images?

The early images of a clean deck in a blue filter were darker than I would have expected for a supposedly bluish deck, but the brightness in IR could be explained by reflectance due to sun angle and reflected IR or, a layer of dust on the deck. This could be cleaned off in the area of the stain resulting in no IR emissions and only deck emissions.

In case one has not guessed, I'm on the clean deck side of the fence. But, I want to know why just this area, just this rover. The investigators say they have seen many instances of streaks and stains. Unless they are holding back, we have seen the same images of the deck they have seen and this is by far the strangest anomaly seen anywhere on the deck of either rover.

Barsoomer

Posts: 344

Reply: 263

Posted: April 30, 2011 12:19 AM

They haven't looked closely at this one. They got excited by some marks before but it always turned out to be nothing. So they are assuming the same this time. Understandable but wrong.

Barsoomer

Posts: 344

Reply: 264

Posted: May 1, 2011 1:10 AM

Psych, if you think the stain could be a cleaning, I am curious to know how you explain it having apparently covered parts of the electrical contacts next to a solar panel? These were clearly light-toned in the images of the clean deck.

Also, if you look at the early posts in this thread, Horton did some "ratio color" comparisons of the stain with the clean deck, showing a clear difference. I'm not sure, but the ratio color approach might at least partially work around some of the issues of relative luminance.

Psych

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Reply: 265

Posted: May 3, 2011 6:49 AM

I'm thinking that, much like sweeping a sidewalk, when the sweeper hits an uneven spot in the pavement, the broom drops some of the sweepings around the spot. The lighter parts of the connections, which are higher than the surface of the deck, may be where the sweepings are being deposited as, whatever is sweeping the deck passes over them and sheds the sweepings.

Psych, re your 262, Yes, it is an exaggeration to say that there are many examples of stain-like patches on the deck. There is the big one next to the sundial, and we have seen one more sharp-edged dark patch that also "grew" once to cover an additional adjacent area. Taking the two "stains" together, they affect far less than 1% of the deck. The deck is a complicated space aerodynamically with lots of edge, and lots of projections of various sizes, but sharp little dark spots are not widely distributed. The wind direction relative to the deck can only be thought of as random, because over the time that the stain has "grown" Oppy drove south, then west, then south, and then east and spent long periods parked in various orientations examining science targets. The seasons of the Mars year have come and gone during this time, an additional reason to expect changes in wind direction.

If the darkness is caused by wind "cleaning" then one has to speculate that the area occupied by the stain must have been "special" from the start - something like an area with hidden residues from imperfect Earth-side cleaning, or some such. Otherwise it is hard to explain why 5 of the 7 darkening events occurred in tiny areas adjacent to existing tiny darkened areas.

Psych

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Reply: 268

Posted: May 3, 2011 6:28 PM

I have tried many experiments in the dust on my pickup by attaching filaments of different styles and watching the patterns evolve as I drive. They most always trace an arc pattern from the anchor point. The most promising seemed to be a very frayed strand of woven nylon. The end frayed to different lengths and while the basic pattern was still an arc, the edge of the arc had mis-shapen edges. I tried to take photos but could never get the lighting right. IMHO there is a very fine web of nylon or fiberglass strands, possibly created by abrasion of that wire loom during the 2007 sandstorm, of a diameter below the .5mm resolution Horton spoke of in post #29 of this thread. This 'web' may never be imaged due to the length of time of the exposures, the resolution of the cameras, combined with what could be constant motion from the wind\breeze. The shape of the 'stain' changes could be due to parts of the 'web' snagging on parts of the rover, then releasing when the wind changes.

Barsoomer

Posts: 344

Reply: 269

Posted: May 3, 2011 11:23 PM

I may have said before that L7 is UV, but actually it is violet, not ultraviolet. UV is below 400 nm.

Reply 265: Why are the dropped sweepings similar in color to the dark swept area rather than having the reddish color of the other dust?

Psych

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Reply: 270

Posted: May 4, 2011 10:24 AM

^^^"Why are the dropped sweepings similar in color to the dark swept area rather than having the reddish color of the other dust?" Yeah that is a problem with that scenario I have not quite worked out. I'm just going with what I have observed of earthly dusts reactions. Perhaps whatever is scrubbing the deck has also removed the 'white' and what was under that now appears dark, yet lightens when dust is redeposited on those surfaces.

I'm also having trouble wrapping my brain around "the stain is blueish" yet it appears dark in many of the L6 430 nm CCD blue frames. I must still not understand filters as well.

Psych

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Reply: 271

Posted: May 4, 2011 11:42 AM

I have been using this site
[link]
along with this page
[link]
to try and grasp what color the light areas of each image would approximately be. The IR of course I just leave as white and tell myself that is heat that I can't really see but it could give me an indication of the temperature I might feel if I touched the object.

Barsoomer

Posts: 344

Reply: 272

Posted: May 4, 2011 2:09 PM

At Martian temperatures, peak thermal emissions would be at over 10,000 nm. So the IR filters are recording reflected solar radiation, not heat, from the object.

Psych

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Reply: 273

Posted: May 4, 2011 2:33 PM

Thanks for that tidbit. I was figuring it might be too cold to actually feel any heat being radiated by the objects. And that it might be only solar IR.

Fred

Posts: 73

Reply: 274

Posted: May 4, 2011 5:21 PM

Barsoomer wrote:
“So the IR filters are recording reflected solar radiation, not heat, from the object.”

If the source of “heat” on the Martian surface is solar, at what point is it non-influential to both diurnal surface objects and ambient air temperature.

Fred

Barsoomer

Posts: 344

Reply: 275

Posted: May 4, 2011 8:19 PM

> ... at what point is it non-influential ...

If I understand your question correctly, solar radiation is never non-influential to object and air temperature. Objects do get warmed by solar radiation, and they do emit thermal radiation as a result. But the radiation they emit in this case has a wavelength above 10 microns (10,000 nm). The filters on the MER pancam are generally insensitive to wavelengths above 1 micron. Even in the case of the single low-pass filter (R7), the thermal radiation is probably swamped by the reflected solar radiation.

Psych

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Reply: 276

Posted: May 4, 2011 8:53 PM

Fred, is that a round about way of saying "how do we know how much of this IR we are seeing is solar reflected from the surface of the object and how much is being radiated by the sun warmed objects?"

Or, is Barsoomer saying that the sun warmed objects are much warmer than the filters can detect?

Psych

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Reply: 277

Posted: May 4, 2011 8:55 PM

Never mind, Barsoomer posted just as I was asking the question and answered it.

Fred

Posts: 73

Reply: 278

Posted: May 5, 2011 8:46 AM

What I am saying is first, reflected solar radiation is not absorbed. What is absorbed is heated. What is reflected is lost and that surface would be cooler. Any reflected “heat” would be an ambient air event if it is to be imaged. You cannot have heat unless there is something to heat or a heat transfer medium. The dark side of Mercury is proof of that.

Psych

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Reply: 279

Posted: May 5, 2011 1:20 PM

Right, right, if its reflected it wasn't absorbed so, how do we tell the difference between reflected and radiated? 'Cause from what I understand from here http://coolcosmos.ipac.caltech.edu/ objects that absorb IR re-radiate it at a lower Hz. I also get the idea that in astronomy NIR is good for detecting dust, is that what they are using it here for?

Fred

Posts: 73

Reply: 280

Posted: May 5, 2011 3:19 PM

No, if was not absorbed or transferred, it was not at all. There is no heat bouncing around unattended.